A liquid ejection head mounted on a liquid ejection apparatus, such as an inkjet printing apparatus, includes an actuator, such as a piezoelectric element, as a generator of energy for ejecting droplets. Such a liquid ejection head is advantageous in that it can eject various types of droplets (ink, for example).
In recent years, liquid ejection apparatuses have been used for diverse purposes, including commercial printing performed by a print on demand (POD) technique. In order to meet the demand for high-speed printing required in commercial printing or the like, an increase in the number of droplets ejected per unit time is required by the liquid ejection head. To this end, the liquid ejection head needs to be driven at high frequencies.
If a liquid that the liquid ejection head ejects on a recordable medium contains a large amount of water, the recordable medium may be deformed (suffer from curling, cockling, or other defects). To prevent such deformation of the recordable medium, using a highly viscous liquid that contains a small amount of water is desirable as the liquid that the liquid ejection head ejects.
However, a highly viscous liquid does not flow easily. Thus, a highly viscous liquid flows slowly in a liquid ejection head that ejects the highly viscous liquid. After the liquid ejection head ejects droplets of the liquid, it takes time to refill the liquid ejection head with the liquid.
In the case of driving the liquid ejection head at high frequencies, there is a need to quickly refill the liquid ejection head with a liquid. If a highly viscous liquid is used here, the liquid ejection head may not be sufficiently refilled with the liquid. If the liquid ejection head is not sufficiently refilled with the liquid, the liquid ejection head may fail to eject droplets.
PTL 1 discloses a technique for quickly refilling a liquid ejection head with a liquid. The liquid ejection head includes individual liquid chambers each connected to an orifice through which droplets are ejected, a common liquid chamber that supplies the liquid to the individual liquid chambers, and a communication portion that allows the common liquid chamber and the individual liquid chambers to communicate with one another.
In the communication portion of the liquid ejection head, multiple triangular prism members each having three sidewalls are vertically disposed. In each prism member, one of the sidewalls faces a corresponding individual liquid chamber and a ridge formed by the other two sidewalls is directed toward the common liquid chamber. Accordingly, the gap between the multiple prism members is narrow on the individual liquid chamber side and wide on the common liquid chamber side.
In this liquid ejection head, the prism members in the communication portion regulate the direction of the liquid flowing from the common liquid chamber to the individual liquid chambers. For this reason, the liquid easily flows from the common liquid chamber to the individual liquid chambers, while the liquid negligibly flows from the individual liquid chambers to the common liquid chamber. Since the liquid ejection head is refilled with the liquid by making the liquid flow from the common liquid chamber to the individual liquid chambers, the liquid ejection head can be quickly refilled with the liquid.
In order that liquid ejection heads can be used for further different applications, liquid ejection heads are required to accept a liquid with a higher viscosity or to be driven at higher frequencies. Specifically, liquid ejection heads are required to eject droplets with a viscosity of 40 cP at a frequency of 50 kHz. In this case, it is difficult for even the liquid ejection head disclosed in PTL 1 to be fully refilled with a liquid flowing from the common liquid chamber to the individual liquid chambers.